In situ electrochemical-ESR measurements of poly(aniline-co-5-aminosalicylic acid) in aqueous solutions

In situ electrochemical-ESR measurements of poly(aniline-co-5-aminosalicylic acid) (PAASA) were carried out in the aqueous solutions with different pH values and at various potentials. The ESR spectra of PAASA in a 0.20 M H2SO4 solution show two types of the ESR signal. However, the ESR spectra of PAASA in a 0.30 M Na2SO4 solution of pH 4.0 show only one ESR signal, but which occurs in a wide potential range of −0.20 to 1.20 V (vs. Ag/AgCl with a saturated KCl solution). To examine the origin of two types of the ESR signal in PAASA, the ESR spectra of poly(aniline-co-o-aminophenol) were also carried out in a 0.20 M H2SO4 solution; its ESR spectra also show two types of the ESR signal at a potential range of 0.20–0.50 V. Therefore, two types of ESR signal can be attributed to unpaired spins situated on a nitrogen atom of aniline unit and the OH free radical from aminophenol unit in the both copolymer chains. A surprising result is that the ESR signal intensity of the deprotonated PAASA is much higher than that of the protonated PAASA in air, in which the experiments were performed under the same weight of PAASA and the same experimental conditions.